Deciphering Multi-Focals

Chances are that if you are over 40, you are probably wearing a multifocal lens. And more than likely you are wearing whatever type of lens your doctor or optician recommended for you the first time you started wearing multifocal lenses. There are options, and there is no one-size fits all. Depending on your specific needs and lifestyle you may choose a different type of multifocal lens then someone else. There are three main types of multifocal lenses: bifocals, trifocals, and no-line bifocals called progressives. And within each type of multifocal there are more options to customize the lens for you.

First off, what are multifocal lenses? It is a lens that has more than 1 focal point. A healthy eye automatically accommodates to allow you to see different distances and auto focuses without us even noticing. Think of a camera that you have to manually focus when you move from something up close to look at the mountains in the distance. Your eyes do that automatically. When we get older, the crystalline lens inside our eye that flexes to focus at different focal points slowly stops flexing as much. In the past you may have glasses for seeing far away, and even though had them on all the time, it was accommodating only for the shape (astigmatism) or length (myopia or hyperopia) of your eye, and the lens inside your eye took care of the “auto focus”. As we age we start to notice that we no longer auto focus and reading starts to become difficult. One solution would be to have one pair of glasses to see far away and another to see up close. But who want switch glasses constantly so that they can see where they are going and then see things up close like their cell phone? Enter multifocal lenses. Essentially they all work the same way in that the lens has different prescriptions (RX) in it at specific places in the lenses so that you can see clearly at different focal lengths. The three common focal lengths that are used (in any combination) are distance (about 36 inches away and beyond), intermediate (about 14 to 36 inches away) and near (about 8 to 16 inches away).

Here is an interactive example of what would be clear in each focal point, as well as some pictures to illustrate how each lens works.

Bifocals:

Diagram of a Bifocal Lens

Diagram of a Bifocal Lens

Bifocals, as the name suggests have two focal points, most commonly distance and near. The one prescription would be in the top of the lens and the other would be on the bottom in a nice half oval shape. The optician making your glasses measures so that the top of the line of the bottom RX is sitting just in line with your bottom eyelid. This will allow you to see in the distance comfortably without the bottom segment getting in your way, while still allowing you to read comfortably when you drop your eyes, as it will line up perfectly with-in that segment. Depending on your circumstances and what you intend to use them for, the line may be placed differently. For instance, if I’m making a pair of sunglass bifocals for a golfer, if I place the line in the regular spot he will not be able to tee off or putt, because when he drops his eyes to look at the ball he will be looking through the near RX in his lens. But if we take out the near RX, he won’t be able to see his scorecard, phone, club menu, etc. The solution? Drop the line low enough so he’ll be able to see his ball comfortably, but he’ll have to raise his head up a little more to see the scorecard through the near RX. He won’t be able to sit down and read a novel comfortably with these glasses, but for golfing they are perfect!

Now you can have bifocals made in any combination of the 3 focal lengths mentioned earlier. For instance, say you are on a computer all day long typing in information from printed documents, like an invoice. Your computer screen is usually in your intermediate focal point and the invoices would be near. If you did distance RX and near RX in your glasses, you would have a hard time seeing your computer screen. You could move further away so that now it’s far enough to use the distance part of your lens or get nice and close and lift your head so that you are looking through the near part of the lens. Neither option is very comfortable. The solution would be to make a pair specifically for work that had intermediate in the top and near in the bottom. There are other options too like trifocals and progressives but we’ll talk about those later.

Bifocals come in different styles, the most common being the flat top 28. The near segment has a flat top and it is 28 mm wide. This suits most bifocal wearer’s needs. You can also get them in a flat top 35, which is 35 mm wide; executive bifocal, which runs the whole way through the lens (looks like two different lens cut in half and stuck together); and rounded bifocal, which looks like a flat top segment turned upside-down. Not all types are available in all optical offices nor are they available in all materials or with all lens options.

  • PRO: It has only 2 focal points. Which means that you get the biggest area for each of the RXs that you decide to put in them. It also means that you can go with a smaller frame than with a progressive or trifocal because you are only trying to fit 2 RXs in a lens instead of 3. Even though theoretically you can go as small as you want, I would not recommend anything that would leave you with less than 10 millimeters for your bifocal segment as you may have a hard time reading through something that small.
  • PRO: Generally the easiest multifocal lens to adjust to. (But high-end progressives lens designs are catching up). Bifocal users almost never have any issues adjusting to the lens design, as it’s set up so that you naturally look through the part of the lens that you are supposed to.
  • PRO: Least expensive of the three main types of multifocal lenses.
  • CON: It has only 2 focal points. Which means that if you have more than a +1.75 add, you will probably notice that you are missing a focal point in your glasses. So either you stick with the near RX and get real close to your computer or you choose the intermediate RX and hold things farther away to read them so you can see things at arm’s length comfortably.
  • CON: You have an abrupt change where the line is at. If you were moving your head around and you looked through the near portion of the lens you would have an “image shift” which can be a little annoying and dizzying.
  • CON: Cosmetically not appealing. Everyone can see that you are wearing multifocal lenses. Which draws attention from you to your lined-glasses-lenses.

Trifocals:

Diagram of a progressive lens

Diagram of a trifocal lens.

Trifocals have, you’ve guessed it, three focal points. These are measured to sit right underneath your pupil and are a little more difficult to fit than bifocals. This will allow you to see fairly comfortably in the distance, have some space for your intermediate and still be able to see up close. The most common design is a 7x 28 Trifocal, which means that the middle segment (the one for the intermediate RX) is 7 mm tall and the width of both the middle and bottom segment is 28 mm. There are some places that offer this in a 7×35 as well, but there are even fewer options available for the trifocal than there are for the bifocal. Usually people who have been wearing a trifocal for a while stick with the trifocal, but not many people anymore start off in a trifocal. In 8 years I have only fit 3 or 4 people into a trifocal and all of them came in to me already wearing a trifocal.

  • PRO: They have 3 focal points. You can see clearly far away, at arm’s length, and up close.
  • CON: You lose some of your distance and reading area. Since the intermediate segment is right below your pupil you have less distance RX in your lens than a bifocal user. And since it is 7 mm tall, it pushes your reading segment down a little bit as well.
  • CON: A lot of lens options are simply not available for trifocals. In our office the only material that we can even get the lens in with anti-glare or polarization is Trivex, which is a type of polycarbonate but much more expensive.
  • CON: You still have a line in your lens. You actually have two. It will take a while to get used to the 2 abrupt changes that you have in your lens.
  • CON: You will need a bigger frame. Since the lens has three Rxs in it you will need a frame large enough to fit all three!

Progressives or no-line bifocals

Diagram of a progressive lens

Diagram of a progressive lens.

By far the most confusing type of multifocal, but the one most optical offices try to put their patients in. It’s also the most expensive of the three. Like trifocals, progressives have 3 main focal points. What differentiates them from their lined brethren is that instead of having an abrupt change from one focal point to the next, they progressively change from one RX to the next. (Hence the name.) This theoretically means that you can see clearly at any distance, not just the major 3 focal distances. Sounds like a win-win scenario. It can be, but depends greatly on 3 things: the optician’s measurements, the type of progressive the patient is fit in, and the expectations that are set with the patient before they order their glasses.

These lenses are measured so that the distance is right in front of your pupil and then it slowly changes into the other RXs. If they are not fit properly then you may feel that you have to tilt your head forward to see far (meaning they are too high) or you have to tilt your head back to see distance clearly (they are fit too low). There is also a minimum fitting height (the distance from your pupil to the bottom of the lens) that differs from brand to brand but is usually 17 or 18 mm. Which means you would need a bigger frame then you would need for a bifocal. Otherwise you will lose part of the near RX. You can get short-fit progressives which allow you to do a minimum height of as low as 13 mil. The catch here is that the progression between the RXs is much quicker and you have a smaller area for each RX section. It might work for some people but drive others batty. Your optician needs to be able to make a specific recommendation for your needs and remind you of the pros and cons of your choice.

The second big factor in how well the progressive lens will work for you is lens design. There are literally hundreds of different options. Some brands are known for making top quality progressive lenses and others not so much. What you want to look for:

  1. Wide channel of view. Since progressives change from one RX to another seamlessly, they run in a narrow corridor in the lens. In spite of what a salesmen may tell you, the prescription does NOT run the whole width of the lens. They are getting better and better every day, but depending on the brand and quality of the design you will notice some distortion and loss of peripheral vision. In the lower quality lenses (like the basic lens that your vision insurance may cover) you will notice it right away. You will have to turn your head right to left to see anything on your sides as supposed to just moving your eyes naturally in the lens. It might be even better for you to wear just a regular bi-focal. With a wider channel you will have a larger intermediate and reading area and you will notice that you can see further in your peripheral than in a standard progressive.
  1. Digitally Surfaced. A digitally surfaced lens is up to 10x more accurate with the RX and has less distortions than from a lens that is not digitally made. This gives you sharper, crisper vision, with easier transitions from each RX in the lens. Digitally surfaced lenses also take into account the distance between your eyes and other measurements to create a pair of lenses that will work together for you instead of one for your right eye and one for your left eye. The corridor in the lens is generally much wider in a digitally surfaced lens. The cost of digitally surfaced lenses has gone down drastically and may only be $100 or so more than a traditional lens. But for the upgraded quality of vision it is well worth it.
  1. Equivalent or better lens design then you already have. If you already wear a progressive lens then your optician should be checking to see what type of design you already have. If, for instance, you have a verliux lens (one of the best progressive maker brands available), you already have a nice wide channel and may even be wearing one of their digital lenses. You would have a very hard time adjusting if your optician put you in a standard progressive design as you would lose the wide channel you are used to, the reading area will be much smaller, and the transitions between the RXs will not be as smooth.

You probably don’t need the best of the best, but make sure that your optician makes a recommendation based on your needs, not just putting you in the lens that they give everybody and definitely not based on how big or small they think your wallet is. Keep in mind that even if you have vision insurance, a good progressive lens design may cost you a few hundred dollars out-of-pocket.

The third thing I mentioned was patient education. If you are not aware of the limitations of the lens you might be unhappy with your decision to wear progressives. There are some people who are “progressive non-adapts”; patients who cannot adjust to wearing progressives. Usually it is an adjustment issue, but most places have a policy where if you can’t adjust to the progressive design they will re-do the lenses in a bi-focal. But it’s generally few and far between. In my experience, with proper training and adjustments most people love their progressive lenses.

  • PRO: Possibility of infinite focal points because of the progressive change in Rxs. Clear vision no matter how far or close you are from what you are looking at!
  • PRO: No image jump. In a lined mulitfocal when your eyes look through that line you experience an image shift as you are now looking suddenly through a different RX.
  • PRO:No line! For people looking to hide the fact that they need multifocal lenses this is a dream come true. Cosmetically they look great and look just like single vision lenses.
  • PRO: A more natural viewing experience. You eyes naturally look through the correct part of the lens when you shift from far to intermediate to near.
  • CON: You will always lose some of your peripheral vision. In a good quality progressive lens design the loss may not even be noticeable, but again it all depends on the lens design you choose.
  • CON: Your reading area will be reduced from that of a bifocal lens. Again in the better lens designs the difference may be negligible, but basic progressive design wearers beware.
  • CON: You will need a bigger frame. Again you could go with a short-fit progressive but you will have to sacrifice something.
  • CON: May take a while to get adjust to. Since there is nothing visible in the lens to tell you where one RX ends and another begins, you may feel like the world is spinning for a few days when you first get them as your brain figures out where to look in the lens for each RX. Once more, the adjustment time is greatly reduced with the digitally surfaced lenses and higher lens designs.

All in all progressives lenses have the greatest probability of fulfilling your multifocal needs, but they may not be the perfect fit for you. Make sure you discuss all of the options with your optician, and then give yourself at least 2 weeks to get used to your new multifocal lenses.

Justin

Justin

Justin is a ABO certified licensed Optician. He has been in the optical industry for 8 years in different states and currently manages Optometry by Thanh-Vi Nguyen in La Quinta, CA. Follow his blog at  www.laquintaeyedoc.com

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5 thoughts on “Deciphering Multi-Focals

  1. Useful article, though I don’t think I’ve ever been offered a choice of “digitally surfaced” or tol what brand a lens will be. One error: I assume when you write “mil” you really mean “mm”. A mil is a common but very different unit: 1/1000 of an inch (about 1/40 mm).

    • Thanks to the correction! All fixed. In some places, (and even some people I’ve worked with), sometimes the optician/sales person doesn’t understand fully or know how to explain the differences in the different brands and options and assumes incorrectly that like single vision, progressive lenses are all the same. Or they may make assumptions as to what someone will want to pay or can afford based on insurance coverage, the pair of glasses they’re already wearing, the frames they picked out, etc. I like to educate my patient and explain the differences between 2 or 3 different types of lenses that will work for them and the cost associated with each. Then they decide which one they want and how much they can afford, and in the long run they are much happier with their lenses.

  2. I’m confused by your diagram of a progressive lens. What are the blue areas to the left and right sides? And the small white circles within the blue areas? And the labels “” and “25”?

    • The Blue areas are “Dead Space” where there is distortion and unclear vision. The area may be bigger or smaller depending on the brand of progressive that you are using. The circles in the lens are etchings that most people will never notice and which tell the dispenser/optician what brand is the lens as well as the reading add… in this case the 25 would mean that it has an add of +2.50.

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